The present invention relates to four-blade rotors, especially for helicopters, wherein the four rotor blades are supported as blade pairs on a rotor head. Each blade pair comprises two rotor blades arranged diametrically opposite each other. The blade support is such that each blade may be adjusted in its blade pitch angle. The individual blades of a blade pair are held together by means of a tensionally strong, torsionally yielding connecting strap forming a tension loaded closed coupling loop. One coupling loop for one blade pair extends in a vertical plane. The other coupling loop for the other blade pair extends in a horizontal plane, whereby the horizontally extending coupling loop passes through the vertically extending coupling loop.
The German Pat. No. 1,531,359 which corresponds to U.S. Pat. No. 3,578,877 describes such a rotor, wherein the loop connecting the respective rotor blade pair passes freely through the rotor head center with a freedom of movement which ensures that the cyclic pitch adjustment or cyclic blade angle adjustment does not cause any twisting of the loop connecting the rotor blades of a blade pair. Both rotor blades of a pair arranged diametrically opposite each other are collectively tilted in the same direction and by the same amount for such blade angle adjustment. Thus, only the collective blade angle adjustment causes a torsional loading of the coupling loop since the loops pass freely through the rotor head. It has been shown in practice, however, that such a rotor system requires central support means for the rotor blade pairs at the rotor head, because of unbalances and vibrations in the axial direction of the rotor blades. Hence, a rotor system such as the one described above has not achieved any practical significance. Until now, the torsionally elastic loops connecting the blades of a blade pair were customarily formed by laminate bundles. A laminate bundle connects a respective rotor blade root to a central member arranged on the rotor head coaxially to the axis of rotation. A disadvantage of such an arrangement is that a twisting or rotary loading of the laminate blade bundle extending as far as the central member, cannot be avoided with each angular movement of the individual rotor blade. German Pat. No. 2,150,741 is an example of such a rotor system.